Re: [Xen-devel] CONFIG_SMP required for save/restore and migration: bug?

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Tue, Aug 27, 2013 at 01:09:41AM +0200, Luca Lesinigo wrote:
> Dear list, I was about to write here seeking for help because my Ubuntu domUs 
> were migrating just fine while my Gentoo ones were just hanging "freezed" 
> after attempting migration, or after saving and restoring on the same node.
> 
> After some more tinkering around, I nailed the issue to my kernel config 
> which was stripped down to the bare minimum: no hardware drivers, no loadable 
> modules... and no SMP. After enabling SMP support my domU were able to 
> migrate without problems. The same happens on 3.2.x and on 3.10.7 kernels.
> 
> Before playing with many different kernel configurations, I searched Xen's 
> wiki and googled around but could not find anything related to this issue.
> 
> So: with my config, non-SMP kernels will freeze after restore, while 
> activating CONFIG_SMP and nothing else will make this problem disappear. 
> Maybe non-SMP kernels are supposed to migrate but there's a software problem, 
> or maybe SMP is a requirement but is not documented (or at least I wasn't 
> able to find it). Maybe it's not CONFIG_SMP but one of its dependencies.
> 
> Either way, I'm writing to the list to report this experience, maybe it is a 
> (software or documentation) bug?

It could also be a dependency issue. Meaning if you undef CONFIG_SMP it won't 
pick up the
rest of the code - say the code needed for migration.

That would be odd and buggy.

If you compare the two .config files what does CONFIG_SMP=y add extra?

Are these PVHVM or PV domUs?

Thanks!

> 
> I'll keep an eye to the list in the next days, if you need any other detail 
> just ask.
> 
> Thank you for developing Xen, keep up with the good work!

Thank you.
> 
> --
> Luca Lesinigo
> 
> 
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